Lipoprotein pigments--their relationship to ageing in the human nervous system. I. The lipofuscin content of nerve cells

Comparative analysis of four nuclei in the human brainstem: Individual differences, left-right asymmetry, species differences

Introduction

It is commonly thought that while the organization of the cerebral cortex changes dramatically over evolution, the organization of the brainstem is conserved across species. It is further assumed that, as in other species, brainstem organization is similar from one human to the next. We will review our data on four human brainstem nuclei that suggest that both ideas may need modification.

Methods

We have studied the neuroanatomical and neurochemical organization of the nucleus paramedianus dorsalis (PMD), the principal nucleus of the inferior olive (IOpr), the arcuate nucleus of the medulla (Arc) and the dorsal cochlear nucleus (DC). We compared these human brainstem nuclei to nuclei in other mammals including chimpanzees, monkeys, cats and rodents. We studied human cases from the Witelson Normal Brain collection using Nissl and immunostained sections, and examined archival Nissl and immunostained sections from other species.

Results

We found significant individual variability in the size and shape of brainstem structures among humans. There is left-right asymmetry in the size and appearance of nuclei, dramatically so in the IOpr and Arc. In humans there are nuclei, e.g., the PMD and the Arc, not seen in several other species. In addition, there are brainstem structures that are conserved across species but show major expansion in humans, e.g., the IOpr. Finally, there are nuclei, e.g. the DC, that show major differences in structure among species.

Discussion

Overall, the results suggest several principles of human brainstem organization that distinguish humans from other species. Studying the functional correlates of, and the genetic contributions to, these brainstem characteristics are important future research directions.

Functional and Neuropathological Evidence for a Role of the Brainstem in Autism

The brainstem includes many nuclei and fiber tracts that mediate a wide range of functions. Data from two parallel approaches to the study of autistic spectrum disorder (ASD) implicate many brainstem structures. The first approach is to identify the functions affected in ASD and then trace the neural systems mediating those functions. While not included as core symptoms, three areas of function are frequently impaired in ASD: (1) Motor control both of the limbs and body and the control of eye movements; (2) Sensory information processing in vestibular and auditory systems; (3) Control of affect. There are critical brainstem nuclei mediating each of those functions. There are many nuclei critical for eye movement control including the superior colliculus. Vestibular information is first processed in the four nuclei of the vestibular nuclear complex. Auditory information is relayed to the dorsal and ventral cochlear nuclei and subsequently processed in multiple other brainstem nuclei. Critical structures in affect regulation are the brainstem sources of serotonin and norepinephrine, the raphe nuclei and the locus ceruleus. The second approach is the analysis of abnormalities from direct study of ASD brains. The structure most commonly identified as abnormal in neuropathological studies is the cerebellum. It is classically a major component of the motor system, critical for coordination. It has also been implicated in cognitive and language functions, among the core symptoms of ASD. This structure works very closely with the cerebral cortex; the cortex and the cerebellum show parallel enlargement over evolution. The cerebellum receives input from cortex via relays in the pontine nuclei. In addition, climbing fiber input to cerebellum comes from the inferior olive of the medulla. Mossy fiber input comes from the arcuate nucleus of the medulla as well as the pontine nuclei. The cerebellum projects to several brainstem nuclei including the vestibular nuclear complex and the red nucleus. There are thus multiple brainstem nuclei distributed at all levels of the brainstem, medulla, pons, and midbrain, that participate in functions affected in ASD. There is direct evidence that the cerebellum may be abnormal in ASD. The evidence strongly indicates that analysis of these structures could add to our understanding of the neural basis of ASD.

In vivo and neuropathology data support locus coeruleus integrity as indicator of Alzheimer's disease pathology and cognitive decline

Several autopsy studies recognize the locus coeruleus (LC) as the initial site of hyperphosphorylated TAU aggregation, and as the number of LC neurons harboring TAU increases, TAU pathology emerges throughout the cortex. By conjointly using dedicated MRI measures of LC integrity and TAU and amyloid PET imaging, we aimed to address the question whether in vivo LC measures relate to initial cortical patterns of Alzheimer’s disease (AD) fibrillar proteinopathies or cognitive dysfunction in 174 cognitively unimpaired and impaired older individuals with longitudinal cognitive measures. To guide our interpretations, we verified these associations in autopsy data from 1524 Religious Orders Study and Rush Memory and Aging Project and 2145 National Alzheimer’s Coordinating Center cases providing three different LC measures (pigmentation, tangle density, and neuronal density), Braak staging, β-amyloid, and longitudinal cognitive measures. Lower LC integrity was associated with elevated TAU deposition in the entorhinal cortex among unimpaired individuals consistent with postmortem correlations between LC tangle density and successive Braak staging. LC pigmentation ratings correlated with LC neuronal density but not with LC tangle density and were particularly worse at advanced Braak stages. In the context of elevated β-amyloid, lower LC integrity and greater cortical tangle density were associated with greater TAU burden beyond the medial temporal lobe and retrospective memory decline. These findings support neuropathologic data in which early LC TAU accumulation relates to disease progression and identify LC integrity as a promising indicator of initial AD-related processes and subtle changes in cognitive trajectories of preclinical AD.

Degeneration of the locus coeruleus is a common feature of tauopathies and distinct from TDP-43 proteinopathies in the frontotemporal lobar degeneration spectrum

Neurodegeneration of the locus coeruleus (LC) in age-related neurodegenerative diseases such as Alzheimer's disease (AD) is well documented. However, detailed studies of LC neurodegeneration in the full spectrum of frontotemporal lobar degeneration (FTLD) proteinopathies comparing tauopathies (FTLD-tau) to TDP-43 proteinopathies (FTLD-TDP) are lacking. Here, we tested the hypothesis that there is greater LC neuropathology and neurodegeneration in FTLD-tau compared to FTLD-TDP. We examined 280 patients including FTLD-tau (n = 94), FTLD-TDP (n = 135), and two reference groups: clinical/pathological AD (n = 32) and healthy controls (HC, n = 19). Adjacent sections of pons tissue containing the LC were immunostained for phosphorylated TDP-43 (1D3-p409/410), hyperphosphorylated tau (PHF-1), and tyrosine hydroxylase (TH) to examine neuromelanin-containing noradrenergic neurons. Blinded to clinical and pathologic diagnoses, we semi-quantitatively scored inclusions of tau and TDP-43 both inside LC neuronal somas and in surrounding neuropil. We also digitally measured the percent area occupied of neuromelanin inside of TH-positive LC neurons and in surrounding neuropil to calculate a ratio of extracellular-to-intracellular neuromelanin as an objective composite measure of neurodegeneration. We found that LC tau burden in FTLD-tau was greater than LC TDP-43 burden in FTLD-TDP (z = - 11.38, p < 0.0001). Digital measures of LC neurodegeneration in FTLD-tau were comparable to AD (z = - 1.84, p > 0.05) but greater than FTLD-TDP (z = - 3.85, p < 0.0001) and HC (z = - 4.12, p < 0.0001). Both tau burden and neurodegeneration were consistently elevated in the LC across pathologic and clinical subgroups of FTLD-tau compared to FTLD-TDP subgroups. Moreover, LC tau burden positively correlated with neurodegeneration in the total FTLD group (rho = 0.24, p = 0.001), while TDP-43 burden did not correlate with LC neurodegeneration in FTLD-TDP (rho = - 0.01, p = 0.90). These findings suggest that patterns of disease propagation across all tauopathies include prominent LC tau and neurodegeneration that are relatively distinct from the minimal degenerative changes to the LC in FTLD-TDP and HC. Antemortem detection of LC neurodegeneration and/or function could potentially improve antemortem differentiation of underlying FTLD tauopathies from clinically similar FTLD-TDP proteinopathies.

Does hearing loss lead to dementia? A review of the literature

Recent studies have revealed a correlation between aging-related hearing loss and the likelihood of developing Alzheimer Disease. However, it is not yet known if the correlation simply reflects the fact that these two disorders share common risk factors or whether there is a causal link between them. The answer to this question carries therapeutic implications. Unfortunately, it is not possible to study the question of causality between aging-related hearing loss and dementia in human subjects. Here, we evaluate the research surrounding induced-hearing loss in animal models on non-auditory cognition to help infer if there is any causal evidence linking hearing loss and a more general dementia. We find ample evidence that induction of hearing loss in animals produces cognitive decline, particularly hippocampal dysfunction. The data suggest that noise-exposure produces a toxic milieu in the hippocampus consisting of a spike in glucocorticoid levels, elevations of mediators of oxidative stress and excitotoxicity, which as a consequence induce cessation of neurogenesis, synaptic loss and tau hyperphosphorylation. These data suggest that hearing loss can lead to pathological hallmarks similar to those seen in Alzheimer's Disease and other dementias. However, the rodent data do not establish that hearing loss on its own can induce a progressive degenerative dementing illness. Therefore, we conclude that an additional "hit", such as aging, APOE genotype, microvascular disease or others, may be necessary to trigger an ongoing degenerative process such as Alzheimer Disease.

Individual variability in the structural properties of neurons in the human inferior olive

The inferior olive (IO) is the sole source of the climbing fibers innervating the cerebellar cortex. We have previously shown both individual differences in the size and folding pattern of the principal nucleus (IOpr) in humans as well as in the expression of different proteins in IOpr neurons. This high degree of variability was not present in chimpanzee samples. The neurochemical differences might reflect static differences among individuals, but might also reflect age-related processes resulting in alterations of protein synthesis. Several observations support the latter idea. First, accumulation of lipofuscin, the "age pigment" is well documented in IOpr neurons. Second, there are silver- and abnormal tau-immunostained intraneuronal granules in IOpr neurons (Ikeda et al. Neurosci Lett 258:113-116, 1998). Finally, Olszewski and Baxter (Cytoarchitecture of the human brain stem, Second edn. Karger, Basel, 1954) observed an apparent loss of IOpr neurons in older individuals. We have further investigated the possibility of age-related changes in IOpr neurons using silver- and immunostained sections. We found silver-labeled intraneuronal granules in neurons of the IOpr in all human cases studied (n = 17, ages 25-71). We did not, however, confirm immunostaining with antibodies to abnormal tau. There was individual variability in the density of neurons as well as in the expression of the calcium-binding protein calretinin. In the chimpanzee, there were neither silver-stained intraneuronal granules nor irregularities in immunostaining. Overall, the data support the hypothesis that in some, but not all, humans there are functional changes in IOpr neurons and ultimately cell death. Neurochemical changes of IOpr neurons may contribute to age-related changes in motor and cognitive skills mediated by the cerebellum.

TDP-43 in ubiquitinated inclusions in the inferior olives in frontotemporal lobar degeneration and in other neurodegenerative diseases: a degenerative process distinct from normal ageing

Ubiquitin immunoreactive (UBQ-ir) inclusions were present to variable extents in the inferior olivary nucleus (ION) in 37/48 (77%) patients with frontotemporal lobar degeneration (FTLD), in 10/11 (91%) patients with motor neurone disease (MND), in 5/5 (100%) patients with Alzheimer's disease (AD), 5/7 (71%) patients with dementia with Lewy bodies, 13/19 (68%) patients with Parkinson's disease, 11/11(100%) patients with Progressive Supranuclear Palsy, 2/6 (33%) patients with Multisystem Atrophy, 1/3 (33%) patients with Huntington's disease and in 14/14 (100%) normal elderly control subjects. In FTLD, UBQ-ir inclusions were present in 26/32 (81%) patients with FTLD-U, in 10/15 (67%) patients with tauopathy, and in the single patient with Dementia Lacking Distinctive Histology. In 13 FTLD-U patients, and in a single AD and in 2 MND patients, the UBQ-ir inclusions had a rounded, spicular or skein-type appearance, and these were also TDP-43 immunoreactive (TDP-43-ir). In all other affected patients in all diagnostic groups, and in control subjects, the UBQ-ir neuronal cytoplasmic inclusions (NCI) were of a conglomerated type, resembling a cluster of large granules or globules, but were never TDP-43-ir. In 3 of the 13 FTLD-U patients with spicular NCI, conglomerated NCI were also present but in separate cells. Double-labelling immunohistochemistry, and confocal microscopy, for UBQ and TDP-43 confirmed that only the spicular UBQ-ir inclusions in patients with FTLD-U, AD and MND contained TDP-43, though in these patients there were occasional TDP-43 immunoreactive inclusions that were not UBQ-ir. Nuclear TDP-43 immunoreactivity was absent in ION in FTLD-U, AD or MND when TDP-43 cytoplasmic inclusions were present, but remained in neurones with UBQ-ir, TDP-43 negative inclusions. The target protein within the UBQ-ir, TDP-43-negative inclusions remains unknown, but present studies indicate that this is not tau, neurofilament or internexin proteins. These TDP-43 negative, UBQ-ir inclusions appear to be more related to ageing than neurodegeneration, and are without apparent diagnostic significance. The pathophysiological mechanism leading to their formation, and any consequences their presence may have on nerve cell function, remain unknown.

Tactile sensitivity of children: effects of frequency, masking, and the non-Pacinian I psychophysical channel

Tactile perception depends on the contributions of four psychophysical tactile channels mediated by four corresponding receptor systems. The sensitivity of the tactile channels is determined by detection thresholds that vary as a function of the stimulus frequency. It has been widely reported that tactile thresholds increase (i.e., sensitivity decreases) as a function of age. However, there is controversial evidence with regard to the progressive loss of sensitivity starting from childhood. In this study, the tactile thresholds of children (n=9, ages 7-11 years) were measured and compared with the thresholds of young adults (n=11, ages 21-27 years). The stimuli consisted of sinusoidal bursts of mechanical displacements, which were applied to the left index fingertips of the participants by using a cylindrical probe (base area=0.126 cm2) without a contactor surround. Absolute thresholds were measured at frequencies of 2, 10, 40, 100, 250, and 500 Hz without masking. The absolute thresholds decreased at high frequencies and were similar to data from the literature except for some discrepancy because of methodological differences. In addition, the threshold of the non-Pacinian I channel was measured at 40 Hz by elevating the thresholds of the Pacinian channel by forward masking. The effects of forward masking in children were similar to results in young adults. In conclusion, there were no significant differences between the tactile thresholds of children and those of young adults at key frequencies: 40 Hz for the Pacinian and non-Pacinian I channels and 250 Hz for the Pacinian channel. These findings contradict the hypothesis that there is gradual loss of tactile sensitivity starting from childhood to early adulthood. The loss of sensitivity due to aging probably is more abrupt and occurs at a later age.

Widespread loss of neuronal populations in the spinal ventral horn in sporadic motor neuron disease. A morphometric study

The cytopathology and loss of neurons was studied in 7670 neurons from the ventral horn of the third lumbar segment of the spinal cord of six sporadic motor neuron disease (MND) patients compared with 7568 neurons in seven age matched control subjects. A modified Tomlinson et al. [Tomlinson BE, Irving D, Rebeiz JJ. Total numbers of limb motor neurones in the human lumbosacral cord and an analysis of the accuracy of various sampling procedures. J Neurol Sci 1973;20:313-27] sampling procedure was used for neuronal counts. The ventral horn was divided in quadrants. Neuronal populations were also classified by the maximum cell diameter through the nucleolus. There was widespread loss of neurons in all quadrants of the ventral horn in MND. Size distribution histograms showed similar neuron loss across all populations of neurons. The dorsomedial quadrant contains almost exclusively interneurons and the ventrolateral quadrant mostly motor neurons. The cytopathology of neurons in the dorsomedial quadrant and of large motorneurons in the ventrolateral quadrant MND was similar. In the dorsomedial quadrant, neuron loss (56.7%) was similar to the loss of large motor neurons in the ventrolateral quadrant (64.4%). The loss of presumed motor neurons and interneurons increased with increased disease duration. There was no evidence that loss of presumed interneurons occurred prior, or subsequent, to loss of motor neurons. We conclude that, in sporadic MND, all neuronal populations in the ventral horn are affected and that interneurons are involved to a similar extent and in parallel with motor neurons, as reported in the G86R transgenic mouse model of familial MND. The increasing evidence of loss of neurons other than motor neurons in MND suggests the need for revising the concept of selective motor neuron vulnerability.

Experimental diabetes accelerates accumulation of fluorescent pigments in rat trigeminal neurons

The purpose of this study was to investigate autofluorescent pigment granules (lipofuscin, ceroid) in the trigeminal neurons (TN) during aging and streptozotocin-induced diabetes. Four young adult male rats were injected with streptozotocin (STZ; 50 mg/kg) to produce diabetes (DM), for comparison with four young uninjected control rats and four aged rats (90 weeks old). Eight weeks after STZ injection, all rats were fixed with 4% paraformaldehyde, and paraffin sections of TN were prepared and observed by fluorescence microscopy. We found the number of neurons with autofluorescent pigments had increased to 30.38% of the total in DM compared to 8.98% in the control group, and 25.36% in the aged rats. The area of autofluorescence within those neurons was 16.84% in aged rats, 13.02% in DM and 4.45% in the controls. Thus, DM caused accelerated accumulation of fluorescent granules in trigeminal neurons, and this change may show that premature aging contributes to neuronal functional decline and morphological change.

The structure of neuromelanin as studied by chemical degradative methods

The biosynthesis, structure and function of neuromelanin (NM), the dark brown melanin-like pigment present in the substantia nigra (SN), are not well characterized, in spite of the possible involvement of NM in the etiology and pathogenesis of Parkinson's disease. NM was isolated from the SN of five non-Parkinsonian human brains. NM and synthetic melanins, employed as models, were characterized by chemical analysis. Alkaline hydrogen peroxide (H2O2) oxidation of NM generated four degradation products, pyrrole-2,3-dicarboxylic acid (PDCA), pyrrole-2,3,5-tricarboxylic acid (PTCA), thiazole-4,5-dicarboxylic acid (TDCA) and thiazole-2,3,5-tricarboxylic acid (TTCA), whose ratios, especially the TTCA to PDCA ratio, indicate that NM is derived mostly from dopamine (DA) with 25% incorporation of cysteine (Cys) in the form of a benzothiazine structure. Hydriodic acid (HI) reductive hydrolysis of NM yielded 4-amino-3-hydroxyphenylethylamine (4-AHPEA) as a marker of cysteinyldopamine (CysDA)-derived units. The 4-AHPEA to PDCA ratio indicates a 21% incorporation of CysDA-derived units into NM. These degradative experiments also suggest that DOPA is not incorporated into NM to a significant extent (approximately 6% the level of DA). It is concluded that the TTCA to PDCA ratio is a useful indicator of CysDA-derived units in NM, and NM consists mainly of DA-melanin with some contribution from CysDA-melanin. The involvement of DA and CysDA as building blocks of NM demonstrates the detoxifying role of NM synthesis, since it prevents the intraneuronal accumulation of DA and CysDA, which would cause toxic effects.

Ageing: definitions, mechanisms and the magnitude of the problem

All multi-cellular organisms undergo change with time. Conception heralds the onset of growth and development, leading to reproductive competence and propagation of the species. With time, organisms age, leading to death as a final end-point. Whilst our knowledge and definitions of growth and reproduction are firmly established, the concept of ageing remains less well understood. One of the reasons for the lack of a singular definition of ageing is that it can be considered in many different ways, according to social, behavioural, physiological, morphological, cellular and molecular changes. Research has led to a number of theories being proposed that may explain the ageing process. In this chapter, we will review some of these theories and address some of the following fundamental questions: What is ageing? How can ageing be measured? When does ageing begin? When is an organism defined as old?

Age-related changes in rat cerebellar basket cells: a quantitative study using unbiased stereological methods

Cortical cerebellar basket cells are stable postmitotic cells; hence, they are liable to endure age-related changes. Since the cerebellum is a vital organ for the postural control, equilibrium and motor coordination, we aimed to determine the quantitative morphological changes in those interneurons with the ageing process, using unbiased techniques. Material from the cerebellar cortex (Crus I and Crus II) was collected from female rats aged 2, 6, 9, 12, 15, 18, 21 and 24 mo (5 animals per each age group), fixed by intracardiac perfusion, and processed for transmission electron microscopy, using conventional techniques. Serial semithin sections were obtained (5 blocks from each rat), enabling the determination of the number-weighted mean nuclear volume (by the nucleator method). On ultrathin sections, 25 cell profiles from each animal were photographed. The volume density of the nucleus, ground substance, mitochondria, Golgi apparatus (Golgi) and dense bodies (DB), and the mean surface density of the rough endoplasmic reticulum (RER) were determined, by point counting, using a morphometric grid. The mean total volumes of the soma and organelles and the mean total surface area of the RER [SN (RER)] were then calculated. The results were analysed with 1-way ANOVA; posthoc pairwise comparisons of group means were performed using the Newman-Keuls test. The relation between age and each of the parameters was studied by regression analysis. Significant age-related changes were observed for the mean volumes of the soma, ground substance, Golgi, DB, and SN (RER). Positive linear trends were found for the mean volumes of the ground substance, Golgi, and DB; a negative linear trend was found for the SN (RER). These results indicate that rat cerebellar basket cells endure important age-related changes. The significant decrease in the SN (RER) may be responsible for a reduction in the rate of protein synthesis. Additionally, it may be implicated in a cascade of events leading to cell damage due to the excitotoxic activity of glutamate, which could interfere in the functioning of the complex cerebellar neuronal network.

The force-frequency relationship is altered in regenerating and senescent rat skeletal muscle

Maximal tetanic tension was elicited at 200, 150, and 150 Hz in control tibialis anterior muscles and at 150, 100, and 100 Hz in 14-day regenerating muscles of young (3 months), adult (18 months), and old (31 months) Fischer 344/Brown Norway F1 rats, respectively. In contrast to young rats, increasing stimulation frequency from 50 to 150 Hz did not elicit significantly greater tetanic tension in control or regenerating muscles of old rats. At higher stimulation frequencies, tetanic fade was prevalent in control and regenerating muscles of adult (250-300 Hz) and old rats (200-300 Hz), but was only present at 14 days of recovery in regenerating muscles of young rats (300 Hz). The decreased efficacy of rehabilitative and physical medicine procedures in adult and elderly patients who have suffered skeletal muscle injury could be explained, in part, by the postulate that tetanic fade is indicative of inadequate synaptic transmission.

Age-related changes in the volume of somata and organelles of cerebellar granule cells

Because cerebellar granule cells are fixed post-mitotic cells, it is expected that they undergo age-related changes like other neurons. To examine this possibility, a stereological study on granule cells of rat neocerebellar cortex was performed for an age spectrum of 2 to 24 months using eight different age groups. The nucleator method, together with point and intersection counting, was used to obtain primary data; arithmetical calculations determined the secondary data. In the soma, the absolute surface area did not change significantly; the volume did, however, exhibit a significant negative linear trend with age. Excluding dense bodies, the absolute volumes of the cytoplasmic components did not vary significantly. The absolute volume of dense bodies displayed a significant positive linear trend with age. Significant positive correlations were detected between the somatic volume and the absolute volume of either mitochondria or ground substance. It was concluded that granule cells showed a fair degree of morphological stability through 18 months. However, the observed changes warn that accompanying physiological alterations may occur, with putative effects on motor coordination.

Suppression of cathepsins B and L causes a proliferation of lysosomes and the formation of meganeurites in hippocampus

Cultured hippocampal slices exhibited prominent ultrastructural features of brain aging after exposure to an inhibitor of cathepsins B and L. Six days of treatment with N-CBZ-L-phenylalanyl-L-alanine-diazomethylketone (ZPAD) resulted in a dramatic increase in the number of lysosomes in the perikarya of neurons and glial cells throughout the slices. Furthermore, lysosomes in CA1 and CA3 pyramidal cells were not restricted to the soma but instead were located throughout dendritic processes. Clusters of lysosomes were commonly found within bulging segments of proximal dendrites that were notable for an absence of microtubules and neurofilaments. Although pyknotic nuclei were sometimes encountered, most of the cells in slices exposed to ZPAD for 6 d appeared relatively normal. Slices given 7 d of recovery contained several unique features, compared with those processed immediately after incubation with the inhibitor. Cell bodies of CA1 neurons were largely cleared of the excess lysosomes but had gained fusiform, somatic extensions that were filled with fused lysosomes and related complex, dense bodies. These appendages, similar in form and content to structures previously referred to as "meganeurites," were not observed in CA3 neurons or granule cells. Because meganeurites were often interposed between cell body and axon, they have the potential to interfere with processes requiring axonal transport. It is suggested that inactivation of cathepsins B and L results in a proliferation of lysosomes and that meganeurite generation provides a means of storing residual catabolic organelles. The accumulated material could be eliminated by pinching off the meganeurite but, at least in some cases, this action would result in axotomy. Reduced cathepsin L activity, increased numbers of lysosomes, and the formation of meganeurites are all reported to occur during brain aging; thus, it is possible that the infusion of ZPAD into cultured slices sets in motion a greatly accelerated gerontological sequence.

Ultrastructural and quantitative study of atypical age-related bodies in the hamster brain

Atypical bodies (ABs), related to aging, are described in the central nervous system of normal aged hamsters. Our study used ultrastructural microscopy and quantitative stereology analysis to study these structures in the hypothalamus and brain stem of 3, 6, 12, 18, 24 and 30 month-old hamsters. We found that these complex bodies have an oval or a round profile with a core of fibrillar or tubular structures rounded by a cytoplasmic crown. We frequently observed accumulations of organelles displaying evidence of degeneration. We found that these structures did not appear until 12 months and their frequency increased with age from 12 to 30 months. Their size can range from 3 to 10 microns, although the median size is 6.5 +/- 0.49 microns in diameter. There is a significant correlation between the quantity of these ABs and the animal's age. Their appearance in both hamster and human normal aging can provide an appropriate animal model to yield more information about the normal aging process. This knowledge of the normal aging process in hamsters may also give new insights into which processes in the human brain occur with normal aging and which ones may be exacerbated as in Alzheimer's disease.

Effect of age on the structure of Meissner corpuscles in murine digital pads

A light and electron microscopic study was performed to determine age changes in Meissner corpuscles. In forepaw digital pads of mice aged to their maximum life expectancy, corpuscles were found to increase in size and complexity until middle age, and then to become smaller, disorganized and lobulated with more advanced age. Nerve terminals at more advanced ages became attenuated with a loss of axonal processes, increased density of the axoplasm, and disordered arrangement of the organelles. Degeneration of axonal mitochondria accelerated with age. Lamellar cell processes investing the axons often become dense and attenuated with fewer plasmalemma-associated vesicles. Basal laminae remained where lamellar processes had disintegrated. Lipofuscin was seen in the lamellar cells only at extremely old age. Extracellular material composed of fine basal lamina substance and collagen fibrils increased remarkably with age. Increased growth and complexity of corpuscles until middle age perhaps compensated for age-associated loss of corpuscles and primary sensory neurons. Changes predominating at older ages are attributed to distal axonopathy and atrophy of the sensory neurons. The probable effect of these age changes on cutaneous sensitivity is considered in relation to current theory of mechanoelectric transduction.

Early cytoskeletal changes as shown by Alz-50 are not accompanied by decreased neuronal activity

The nucleus tuberalis lateralis (NTL) is located in the basolateral part of the hypothalamus and is only present as a well-delineated nucleus in human and higher primates. In Alzheimer's disease (AD), NTL neurons show strong early cytoskeletal alterations, as revealed by the antibody Alz-50, but practically no senile plaques or neurofibrillary tangles. To study whether the activity of NTL neurons decreases when cytoskeletal changes appear, i.e., during aging and in AD, we applied a polyclonal antibody raised against the medial cisternae of the Golgi apparatus (GA). The size of the GA and the cell profile of NTL neurons, two established parameters for neuronal activity, were measured by an image analysis system. No significant change in the size of the profiles of the GA or of the neurons was observed in this nucleus during aging or AD. Earlier studies have shown that there is no decrease in cell number in the NTL in AD. We conclude that in the NTL an early hallmark of AD, i.e., cytoskeletal changes as stained by Alz-50, does not correlate with decreased neuronal activity, as reflected by the size of the GA, nor with a decrease in cell number. In addition, we found that the very early occurring and abundant presence of lipofuscin in NTL neurons does not go together with decreased neuronal activity.

Effects of AETT-induced neuronal ceroid lipofuscinosis on learning ability in rats

The behavioral effects of ceroid-lipofuscin accumulation, induced by intraperitoneal administration of acetyl-ethyl-tetramethyl-tetralin (AETT) in Wistar rats for 3 months, were examined in the present studies. A significant increase in neuronal ceroidlipofuscin was demonstrated neuropathologically as well as morphometrically. Although the AETT-intoxicated rats showed neither alteration of locomotor activity nor shock sensitivity, a significant impairment of learning ability, especially an acquisition trial in passive avoidance tests, was observed. Results of the present studies indicate the possibility that a diffuse lipofuscin accumulation causes a learning impairment in rats. The results also imply the possibility of a significant role of age-related lipofuscin accumulation in the dementing processes of human especially in the elderly.

Absolute number and size of pigmented locus coeruleus neurons in young and aged individuals

Significant loss of noradrenergic neurons of the locus coeruleus in aging and Alzheimer's disease has been reported. The interpretation of these analyses, however, is problematic because of the model- and assumption-based nature of conventional sampling and estimation techniques. In the present study, unbiased stereological methods were used to estimate the total number and mean cell volume of pigmented neurons of the locus coeruleus in the brains of young and aged nondemented persons. No side-to-side differences are seen, and there is no change in pigmented cell number or size in the locus coeruleus of nondemented older persons as compared with that of young individuals. In light of previous studies that show severe locus coeruleus cell loss in Alzheimer's disease, these data support further critical investigations into the possible protective role of noradrenaline in normal cognitive functions and emphasize the importance of avoiding methodological bias in quantitative neuroanatomical studies.

Age-related hearing impairment in senescence-accelerated mouse (SAM)

The auditory brainstem response and histopathology of the cochlea were investigated in an accelerated senescence-prone strain, SAM-P/1 mice and a senescence-resistant strain, SAM-R/1 mice. Each strain displayed an age-related auditory loss expressed as elevated thresholds similar to human hearing loss in that high-frequency losses occurred earlier than middle- or low-frequency losses. SAM-P/1 showed a more rapid decline of hearing with age than did SAM-R/1. Interpeak intervals I-III and I-IV were prolonged with age in both strains, especially at high frequency. The prolongation was more marked in SAM-P/1 than in SAM-R/1. The decrease in amplitude of wave I observed in both strains was greater in SAM-P/1 than in SAM-R/1. The auditory function assessed by thresholds, interpeak intervals and amplitudes of wave I in SAM-P/1 at 12 months of age corresponded roughly to that in SAM-R/1 at 20 months of age. In morphological studies, there was an age-related decrease in the cell density as well as in the size of spiral ganglion neurons in both strains, but these changes were more pronounced in SAM-P/1 than in SAM-R/1. These results reveal that age-related hearing impairment associated with morphological changes in the cochlea is manifested earlier and progresses more rapidly in SAM-P/1 than in SAM-R/1. Thus, the SAM-P/1 strain should prove useful as a model of presbycusis.

Lysosomal abnormalities in degenerating neurons link neuronal compromise to senile plaque development in Alzheimer disease

Antibodies to the lysosomal hydrolases, cathepsins B and D and beta-hexosaminidase A, revealed alterations of the endosomal-lysosomal system in neurons of the Alzheimer disease brain, which preceded evident degenerative changes and became marked as atrophy, neurofibrillary pathology, or chromatolysis developed. At the earliest stages of cell atrophy, hydrolase-positive lysosomes accumulated at the basal pole and then massively throughout the perikarya and proximal and proximal dendrites of affected pyramidal neurons in Alzheimer prefrontal cortex and hippocampus, far exceeding the changes of normal aging. Secondary lysosomes as well as tertiary residual bodies (lysosomes/lipofuscin) increased implying stimulated, autophagocytosis and lysosomal system activation. Less affected brain regions, such as the thalamus, displayed similar though less extensive alterations. Certain thalamic neurons exhibited a distinctive lysosome-related abnormality characterized by the presence of cell surface blebs of varying size and number filled with intense hydrolase immunoreactivity. At more advanced stages of degeneration in still intact neurons, hydrolase-positive lipofuscin, particularly in the form of abnormally large aggregates, nearly filled the cytoplasm. Similar lipofuscin aggregates were observed in abundance in the extracellular space following cell lysis and were usually associated with deposits of the beta-amyloid protein. Degenerating neurons and their processes were the major source of these aggregates within senile plaques which contained high concentrations of acid hydrolases. We have shown in previous studies that these lysosomal hydrolases in plaques are enzymatically-active. The persistence of lysosomal structures in the brain parenchyma after neurons have degenerated is a striking and potentially diagnostic feature of Alzheimer disease which has not been observed, to our knowledge, in other degenerative diseases. The lysosomal response in degenerating Alzheimer neurons represents a probable link between an early activation of the lysosomal system in at-risk, normal-appearing neurons and the end-stage contribution of lysosomes to senile plaque formation and emphasizes a slowly progressive disturbance of the lysosomal system throughout the development of Alzheimer disease.

Effect of soft diet and aging on rat masseter muscle and its motoneuron

To determine the effect of a soft diet and aging on the masticatory motor unit, we investigated the morphologic and metabolic properties of the superficial masseter muscle and its motoneurons in rats. Twenty rats were divided into four groups of five rats: rats fed a hard diet until 4 months after birth (hard, young), rats fed a soft diet until 4 months after birth (soft, young), rats fed a hard diet until 22 months after birth (hard, old), and rats fed a soft diet until 22 months after birth (soft, old). The diameter of the fast-twitch oxidative glycolytic muscle fiber was significantly smaller in the soft than the hard, and in the old than the young groups. The glycolytic enzyme (phosphofructokinase) activity of the muscle was significantly weaker in the old than the young group. There was no significant difference in soma diameter of the motoneurons between the soft and hard group, while the diameter was significantly larger in the old than in the young group. There was no significant difference in NADH-diaphorase activity of the motoneurons between the soft and hard group, while significantly less activity was demonstrated in the old than in the young group. The reduction in motor unit activity caused by the soft diet is considered to influence the morphologic and metabolic properties in the superficial masseter muscle but not in its motoneurons. The reduction in the oxidative enzyme activity of motoneurons with aging may occur regardless of the reduction in motor unit activity.

Ultrastructural observations on neuronal lipofuscin (age pigment) and dense bodies induced by a proteinase inhibitor, leupeptin, in rat hippocampus

The ultrastructure of lipofuscin (age pigment) and dense bodies induced by intraventricular administration of leupeptin, a cysteine proteinase inhibitor, were investigated in the neurons of rat hippocampal dentate gyrus. Four-day treatment with leupeptin (0.5 mg/day) rapidly caused a considerable accumulation of intracytoplasmic dense bodies and swelling of neuronal processes. We demonstrated, as inner structures of the pigments, that penta-laminar structure with a thickness of 12-13 nm and finely granular matrix were exactly common to the leupeptin-induced dense bodies and lipofuscin granules. Furthermore, the transitional stages from lysosomes into the dense granules were observed in the neurons of the leupeptin-treated rats. On the other hand, some morphological differences between the leupeptin-induced dense bodies and lipofuscin granules have been shown: (1) distribution in different cell types, (2) intracytoplasmic location, (3) tendencies to associate with vacuoles, and (4) electron density. The present findings suggested that the decline of the lysosomal protein degradation could play a role in lipofuscinogenesis, especially in the genesis of their electron-dense portion, but some other mechanisms might participate in the formation and accumulation of lipofuscin with aging.

Routes of excretion of neuronal lysosomal dense bodies after ventricular infusion of leupeptin in the rat: a study using ubiquitin and PGP 9.5 immunocytochemistry

To determine the rate and routes of removal of lysosomal, lipofuscin-like dense bodies from neurons, the protease inhibitor, leupeptin, was infused into the lateral ventricle of rats for up to nine days. After seven days a number of animals were then allowed to recover. The formation and later disappearance of dense bodies was followed by morphology and immunocytochemistry. After 48 h of infusion lysosomal dense bodies in large numbers appeared in cortical, hippocampal and cerebellar neurons, which also showed increased ubiquitin immunoreactivity, as well as in other cell types. By 3-4 days ubiqutin-immunoreactive dense bodies were equally distributed between neurons and astroglia. After seven to nine days of infusion ubiquitin immunoreactive dense bodies filled neuronal perikarya, dendrites and expanded initial segments of many axons and were abundant in glial processes. All dense bodies studied by electron microscopy were ubiquitin immunoreactive. After four days of recovery dense bodies were markedly fewer in neuronal perikarya, and virtually all were now within glial processes. From 7 to 28 days of recovery, when most neurons appeared normal, lipofuscin bodies remained in axon initial segments and in reduced numbers in glial processes, particularly around blood vessels and beneath the pia of hippocampus and of cerebellar cortex. Thus, neurons probably have a steady passage of short lived proteins through the lysosomal excretory pathway. The observed temporal sequence of events on recovery suggests that secondary lysosomes probably pass rapidly from neuronal perikarya and dendrites to astrocytes and thus to the vascular bed or pia-arachnoid. The mechanism of cell-to-cell transfer is not clear from this study.

Lipofuscin is a photoinducible free radical generator

Despite the association between high concentrations of the age pigment lipofuscin and various age-related pathologies, there is contention as to whether or not the intracellular accumulation of such granules has an adverse effect on cell function. In this paper, we present evidence to indicate that lipofuscin is a photoinducible free radical generator. White light irradiation of lipofuscin granules resulted in the production of superoxide anions, their rate of production increasing with increased light intensity. This effect appeared to be maximal in the blue light region of the spectrum. We speculate that lipofuscin could be detrimental to bodily functions through free radical generation initiated either by light or interaction with endogenous free radicals.

Age-related decline in multiple unit action potentials of CA3 region of rat hippocampus: correlation with lipid peroxidation and lipofuscin concentration and the effect of centrophenoxine

Changes in lipid peroxidation, lipofuscin concentration, and multiple unit activity (MUA recorded in conscious animals) in the CA3 region were studied in the hippocampus of male Wistar rats aged 4, 8, 16, and 24 months. The lipid peroxidation and lipofuscin concentration were increased with age. The MUA, however, declined with age. Correlational analyses were performed for the four age groups to determine the relationship between the age-associated decline in MUA with the age-related alterations in lipid peroxidation and lipofuscin concentrations. The age-related increase in lipid peroxidation correlated positively with the age-associated increase in lipofuscin concentration. The age-related increases in lipid peroxidation and lipofuscin concentration correlated negatively with the changes in MUA. Since lipid peroxidation may affect neuronal electrophysiology, our data suggested that age-related increase in lipid peroxidation may contribute to an age-associated decline in neuronal electrical activity. Centrophenoxine effects were studied on the three above-mentioned age-associated changes in the hippocampus. The drug had no effect on all three parameters in 4- and 8-month-old rats. In 16- and 24-month-old rats, however, the drug significantly increased the MUA but concomitantly decreased lipofuscin concentration and lipid peroxidation. Correlational analyses of the data on MUA, lipid peroxidation and lipofuscin concentration from the centrophenoxine-treated animals showed that the drug-induced diminution in both lipofuscin and lipid peroxidation was significantly correlated with the drug-induced increase in MUA. The differential effect of the drug in younger (4-8 months) and older (16-24 months) animals indicated that the stimulation of MUA was clearly associated with concomitant decrease in lipid peroxidation and lipofuscin concentration.

The lysosomal system in neuronal cell death: a review

The lysosomal system has often been considered a prominent morphologic marker of distressed or dying neurons. Lysosomes or their constituent hydrolases have been viewed in different neuropathologic states as either initiators and direct agents of cell death, agents of cellular repair and recompensation, effectors of end-stage cellular dissolution, or autolytic scavengers of cellular debris. Limited data and limitations of methodology often do not allow these potential roles to be discriminated. In all forms of neurodegeneration, it may be presumed that lysosomes ultimately rupture and release various hydrolases that promote cell autolysis during the final stages of cellular disintegration. Beyond this perhaps universal contribution to cell death, the degree to which the lysosomal system may be involved in neurodegenerative states varies considerably. In many conditions, morphologic evidence for activation of the lysosomal system is minimal or undetectable. In other cases, lysosomal activation is evident only when other morphologic signs of cell injury are also present. This level of participation may be viewed as either an attempt by the neuron to compensate for or repair the injury or a late-stage event leading to cell dissolution. The early involvement of the lysosomal system in neurodegeneration occurs most commonly in the form of intraneuronal accumulations of abnormal storage profiles or residual bodies (tertiary lysosomes). Very often the lysosomal involvement can be traced to a primary defect or dysfunction of lysosomal components or to accelerated or abnormal membrane breakdown that leads to the buildup of modified digestion-resistant substrates within lysosomes. Because they are often striking, changes in the lysosomal system are a sensitive morphologic indicator of certain types of metabolic distress; however, whether they reflect a salutary response of a compromised neuron or a mechanism to promote cell death and removal of debris from the brain remains to be established for most conditions. Factors that may influence the lysosomal response during lethal neuronal injury include species differences, stage of neuronal development, duration of injury and pace of cell death. The lysosomal system may be more closely coupled to certain forms of neuronal cell death in lower vertebrate or invertebrate systems than in mammalian systems.

Effect of partial denervation on motor units in the ageing rat medial gastrocnemius

The ageing neuromuscular system is thought to undergo a continual process of reorganization as motoneurones are lost and surviving motor nerves reinnervate neighbouring denervated muscle fibres. However, the extent to which collateral reinnervation is able to compensate for neural deficits in the ageing individual is unknown. The ability of the senescent motoneurone to increase the size of its peripheral field was therefore investigated following transection of the right L5 ventral root in male Sprague Dawley rats aged 775 +/- 50 days. This procedure resulted in an extensive partial denervation of the right medial gastrocnemius muscle. After a recovery period of between 28 and 31 days the isometric contractile properties of surviving motor units were compared to control motor units from both the contralateral muscle and a group of unoperated control animals aged 791 +/- 39 days. Motor unit force was found to be unchanged after partial denervation and the absence of any alteration in motor unit size was confirmed by histological analysis. However, the time course of the isometric twitch was significantly longer for both fast and slow motor unit types and the conduction velocity of motoneurones innervating fast units was decreased following partial denervation. These results demonstrate that senescent motor nerves are unable to substantially increase the size of their peripheral fields by extensive collateral reinnervation.

Morphometry of spinal motor neurons in amyotrophic lateral sclerosis with special reference to chromatolysis and intracytoplasmic inclusion bodies

Lewy body-like hyaline inclusions (LBI), Bunina bodies (BB) and central chromatolysis are characteristic neuropathological features of spinal motor neurons in amyotrophic lateral sclerosis (ALS). Using histometric methods, we studied the spinal motor neurons of 4 patients with sporadic ALS and 3 neurological control patients to determine the possible relationship between these neuropathological features and cytoplasmic, nuclear and nucleolar size. In an ALS patient with a very rapid clinical course, many neurons with LBI were observed. Enlargement of nucleolar size and the nucleolar/nuclear ratio of neurons with LBI or BB were the only histometric difference compared to those of normal-appearing neurons. In ALS patients with an average clinical course, the number of neurons with LBI was lower, the number of neurons with BB was higher, and the nuclear and nucleolar sizes were smaller than those of normal-appearing neurons, particularly in chromatolytic neurons without LBI or BB. These data raise the possibility that motor neurons with LBI may represent an early stage in the neurodegenerative process, when the rate of protein synthesis is elevated as evidenced by their larger nucleolar size. Thus, the causative agent(s) of ALS may initially stimulate protein synthesis while in turn leading to down regulation of certain luxury function genes, culminating in neuronal dysfunction and death.

Lifelong ethanol consumption enhances the age-related changes in rat sympathetic neurons

The effects of aging and chronic ethanol administration on the histochemical and morphometric features of rat superior cervical ganglion were studied in a rat strain selected for voluntary alcohol consumption. Ethanol was administered to the experimental group ad libitum (10% v/v in drinking water) from 3 months to 28 months of age, the average ethanol intake being 6.4-5.4 g/kg per day. The sympathetic neurons of the ethanol consuming rats showed several signs of enhanced degeneration, e.g. decreased neuronal packing density, increased amount of age-pigment and decreased intensity of catecholamine histofluorescence and tyrosine hydroxylase immunoreactivity. The results may indicate a selective vulnerability of peripheral sympathetic neurons rather than a universal accelerated aging due to chronic ethanol exposure.

Fabry disease: immunocytochemical characterization of neuronal involvement

Fabry disease is an X-linked glycosphingolipid storage disease caused by deficiency of alpha-galactosidase. Storage of globotriaosylceramide, also known as ceramide trihexoside, is maximal in blood vessels but also occurs in neurons. We performed neuropathological histochemical studies on the brains and spinal cords of 2 patients with confirmed Fabry disease. Luxol fast blue-positive deposits were found in blood vessels throughout the central and peripheral nervous system and within selected neurons in spinal cord and ganglia, brainstem, amygdala, hypothalamus, and entorhinal cortex. Regions adjacent to involved neuronal groups, including nucleus basalis, striatum, globus pallidus, and thalamus, were spared. Electron microscopy showed lamellar cytoplasmic neuronal inclusion bodies. Using a monoclonal antibody reactive with ceramide trihexoside, we found more extensive neuronal deposition than evident by Luxol-fast blue staining and new areas of neuronal storage in the spinal cord and cerebral cortex. Blood vessels throughout the nervous system were strongly immunoreactive. The highly selective pattern of neuronal involvement we found suggests that glycosphingolipid exposure, uptake, or catabolism varies greatly with respect to neuronal morphology and distribution. The degree of toxicity to neurons and the clinical significance of this neuronal storage remains to be defined.

No relationship between the age-related decrease in prostacyclin production and the level of intracellular lipid peroxidation in human umbilical vein endothelial cells in culture

Some investigators have speculated that a decrease in prostacyclin production observed during ageing of endothelial cells is caused by an increase in intracellular lipid peroxide. We checked this speculation using an in vitro model to study the ageing of human vascular endothelial cells. For this purpose we determined the levels of intracellular lipid peroxide of endothelial cells at various culture ages, and found that the level of intracellular lipid peroxidation did not increase during in vitro ageing. Amounts of intracellular lipid peroxide also differed depending on the growth phase, the addition of heparin and the strain of endothelial cells, but the cells producing prostacyclin at a low level did not necessarily contain larger amounts of intracellular lipid peroxide. Therefore, we postulate that the age-related decrease in prostacyclin production is not due to an increase in the amount of intracellular lipid peroxide as a function of age.

Brain aging and Alzheimer's disease, "wear and tear" versus "use it or lose it"

In organs other than the brain, cell activation seems to increase "wear and tear," e.g., by increased free-radical formation, and so to cause an increased rate of aging. However, activation of nerve cells within the physiological range seems to lead to maintenance of neurons during aging and in Alzheimer's disease, possibly by preferentially stimulating the action of protective mechanisms such as DNA repair. This "use it or lose it" principle might explain why certain neurons degenerate in aging or Alzheimer's disease while others do not, and why recovery of various neuronal systems during aging has been obtained by restoration of the missing stimulus. Consequently, neuronal activation might provide a means of prolonging its optimal function for the full length of our natural life span.

Histochemical and ultrastructural observations on brown degeneration of human intervertebral disc

Thirty-eight fresh human intervertebral discs collected during anterior interbody fusion surgery were histochemically and ultrastructurally analyzed for pigments. Macroscopically, five stages of degeneration were classified according to the color, fibrosis, and fragility of the nucleus pulposus of the discs. In order to demonstrate lipofuscin granules, specimens were subjected to special staining procedures, including carbol fuchsin lipofuscin stain, the Schmorl's reaction, and autofluorescence. Lipofuscin granules were distributed from the inner layer of the annulus fibrosus to the nucleus pulposus. Such granules were numerous in cases of slight or severe degeneration, whereas fewer granules were found in cases of moderate degeneration. However, the stage of macroscopic degeneration of the intervertebral disc did not necessarily correlate with the incidence of lipofuscin granules. By ultrastructural observation, the morphological features of the components of the intervertebral disc and the ultrastructure of the lipofuscin granule were clarified. The ultrastructure of the "brown degeneration" disc exhibited markedly increased amorphous electron-dense bodies located among collagen fibrils in the matrix.

Ageing changes in the transplants of fetal substantia nigra grafted to striatum of adult rat

Fetal nigral neurons from 16 and 17 gestational days were transplanted into the intact striatum of adult rat. On different post-transplantation days (30-360 days), the structural and immunohistochemical details of the transplants were studied. The grafted neurons matured and showed phenotypical characteristics comparable to that of normal nigral neurons in adult rats until 180 days. Tyrosine hydroxylase-positive neurons were seen not only in the transplant but also in the adjacent host striatum. Tyrosine hydroxylase-positive fibres were also seen extending for a short distance into the host striatum. A large number of synapses in the transplants were of asymmetric type, containing clear round vesicles. These synapses resembled the few intrinsic type present in the normal substantia nigra. On the other hand, the predominant type 2 synapses with pleomorphic vesicles in the normal nigra were infrequently encountered in the transplants. On the 300th day, the cytoplasm of a few of the neurons showed ageing changes in the form of clear spaces, paucity of organelles especially rough endoplasmic reticulum, membrane-bound vacuoles and increase in the lipofuscin population. In addition, localized thickening of the soma and the dendrites were seen in relation to randomly distributed neurons. By 360 days, more than one quarter (26%) of the total neurons showed these changes indicating ageing. The number per unit volume of normal neurons decreased significantly when compared to the transplants on 60 and 90 days. In the substantia nigra of age-matched control, except for an increase in the lysosomal population, other ageing changes were not detectable. The neurons of intact substantia nigra of the host rat, chronologically 4-8 months older than the transplanted neurons, also appeared normal but for lipofuscin granules. The present study provides morphological evidence for rapid ageing of neurons in the long term nigral transplants. These observations raise fresh doubts regarding permanent survival of grafted neurons in the host brain. Studies so far conducted are after prior nigral lesions. Trophic factors following lesions of the host tissue may have influenced the long term survival of the transplanted neurons. On the other hand, such changes may have been missed since no detailed morphological investigations of the long term transplants have been done so far.

Age-related decrease in sympathetic sprouting is primarily due to decreased target receptivity: implications for understanding brain aging

Aging of the nervous system is characterized by reduced anatomical plasticity. The cause of this decreased plasticity is not known because it is usually not possible to distinguish between extrinsic and intrinsic factors that affect neuronal growth. One example of age-related reduced neuronal plasticity that is amendable to such analysis is the growth of sympathetic axons into the rat hippocampal formation following septal denervation. This sprouting response can be elicited throughout the lifespan of the rat but is drastically reduced in aged animals. The age-related reduction in ingrowth could theoretically be due to decreased receptivity of the target (reduced trophic support or increased inhibition of growth), decreased responsivity of the sympathetic neurons or a combination of both factors. In order to test the relative contributions of the age of the target tissue and the age of the sympathetic neurons to the reduced growth observed in aged animals, superior cervical ganglia were transplanted from young animals into old animals (y/o) and from old animals into young animals (o/y) as well as autologously within the same animals (y/y and o/o). The extent of sympathetic ingrowth and the survival of transplanted neurons were assessed with fluorescence histochemical methods. The extent of ingrowth was significantly greater in young hosts compared with old hosts regardless of the age of the donor. In addition, the survival of transplanted neurons was greater in younger hosts than in aged hosts regardless of donor age. These results indicate that sympathetic ingrowth is reduced in aging primarily because of decreased receptivity of the hippocampal target tissue.

Neuronal population of area 4 during the life span of the rhesus monkey

One right or left area 4 of each of 19 rhesus monkeys, ranging in age from 1 day to 35 years, was processed (frozen sectioned at 30 or 40 microns) for light microscopic analysis to assess age-related changes in the neuronal population. All neurons were examined regardless of their size. In addition, Betz cells were analyzed separately; to be regarded as Betz cells, pyramidal somata had to display a minimum height of 38 microns. A significant loss of approximately one-third was observed in the total number of neurons in maturing monkeys (less than 5.5 years). In contrast, in maturing rhesus monkeys significant increases with age were observed in the mean number of Betz cells, and in the means of Betz cell area, height, width, perimeter, and estimated volume. In adult monkeys (greater than 4.5 years), no age-associated loss of neurons was observed. Also, no loss of Betz cells occurred, although the perimeter, area, and estimated volume of Betz cells decreased slightly, but significantly, with increasing age in adult monkeys. Lipofuscin granules were discernable in Betz cells beginning at the age of 5 years and their number increased with increasing age. In the older rhesus monkeys, the lipofuscin granules were so large and numerous that in some Betz cell somata they displaced the nucleus from its usual location in the center of the cell. No age-related change in thickness of area 4 was found.

A method for the relative quantification of lipofuscin based on a computer image analysis system

The accumulation of lipofuscin in neurons is the best recognized microscopic alteration of the aging brain. The broad spectrum which characterizes this progressive accumulation of pigment has made necessary the use of quantitative methods for its assessment. Present day techniques for the quantitation of lipofuscin (e.g. fluorescent microspectrophotometry and planimetry) are cumbersome, rely on manual techniques and may be limited by fluorescent artifacts. In this article we report a computer image analysis method for the relative quantification of lipofuscin in slides stained with a modified aldehyde fuchsin stain. The method preserves the topography of the pigment, is not limited by artifacts due to fluorescence, and has excellent inter-rater reliability.

Neuronal lipopigment: a marker for cognitive impairment and long-term effects of psychotropic drugs

Lipopigment, identifiable in the fluorescence microscope, is thought to be cellular debris partly derived from free-radical-induced peroxidation of cellular constituents. The volume of neuronal lipopigment has been positively correlated with advancing age, Alzheimer dementia, and the neuronal ceroidoses, while various changes in neuronal lipopigment have been reported in association with the chronic administration of dihydroergotoxine, ethanol, phenytoin, centrophenoxine, and chlorpromazine. An increase in the volume of neuronal lipopigment may indicate increased functional activity of the cell, impaired removal of pigment or anoxia. Chronic administration of agents which can be correlated with decreased neuronal lipopigment in animal models might protect neuronal function against any adverse effects associated with (but not necessarily resulting from) lipopigment accumulation in normal ageing, anoxia, or certain degenerative diseases. Long-term studies of the prophylactic use of such agents, or of drugs which neutralise free radicals, may be indicated. Other clinical applications of such drugs may include protection against the effects of free radicals formed during periods of oxygen deprivation.

Spiral ganglion cell density in young and old gerbils

The Mongolian gerbil, like other mammalian species, has a decreased number of spiral ganglion cells as a function of age. This loss of cells was first seen in 24- to 30-month old animals in the basal end of the ganglion. In the oldest individuals the apical end of the ganglion was also affected. There were approximately 15-25% fewer cells in the affected areas in the 36- to 42-month old animals. In the oldest animals degeneration of the stria vascularis was seen in the apical turn and some degenerative changes in the organ of Corti were seen throughout the length of the cochlear duct. The aging pattern in the gerbil cochlea, is similar to that described for other species. Vacuoles, previously described in the gerbil cochlear nucleus, were also seen in the auditory nerve within the modiolus, but central to the Schwann-glial border in all animals. Vacuoles were not present within the spiral ganglion or the peripheral processes of the ganglion cells. Because the ganglion cell axons should be similar on either side of the Schwann-glial border, but the vacuoles were confined to the central nervous system, it is concluded that the degenerative process affects glial cells as opposed to neurons.

Age-related alterations in noradrenergic input to the hippocampal formation: structural and functional studies in intraocular transplants

Intrinsic versus extrinsic determinants of age-related alterations in hippocampal noradrenergic transmission were investigated using intraocular allografts in rats. Three groups of animals were examined: young hippocampal transplants in young hosts, old transplants in old hosts and young transplants in old hosts. Postsynaptic sensitivity to noradrenaline (NA) was measured by extracellular recordings of spontaneous activity and superfusion with known concentrations of catecholamines in the anterior chamber of the eye. Hill plots demonstrated that the dose-response relationships of NA-induced depressions were linear and parallel in the 3 groups. Aged hippocampal grafts displayed a highly significant subsensitivity to NA of one order of magnitude. The EC50 for this group was 203.1 microM as compared to 29.2 in young grafts. Young intraocular grafts in old hosts responded similarly to transplants in young hosts, with an EC50 of 32.4 microM for the depressant actions of NA. Collaterals of the host iris sympathetic ground plexus invaded the hippocampal grafts. The density of this noradrenergic innervation was estimated by immunohistochemistry for tyrosine hydroxylase. A slightly increased density and fluorescence intensity of the noradrenergic fibers were observed in the old transplants as compared to the young transplants in young and old hosts. This was correlated with a significantly (P less than 0.01) increased content of NA in old transplants, as measured with high performance liquid chromatography. The old transplants also contained a large number of autofluorescent lipofuchsin granules, which were absent in the young transplants, regardless of the recipient age. Taken together, these results suggest the existence of alterations in pre- as well as postsynaptic noradrenergic mechanisms in the aging hippocampus. These changes were dependent on transplant age rather than host age, thus suggesting an involvement of intrinsic rather than extrinsic determinants in this model system.